In eukaryotes the genetic basis for regulation of gene expression is not well understood. We propose the investigation of beta-glucuronidase in Drosophila as a model for the genetic analysis of such regulation. The studies proposed follow those initiated in mice and should allow us to genetically dissect the steps of final enzyme expression including rate of synthesis, time of appearance, intracellular localization, nature and extent of post-translational modifications and rate of degradation. The increased sophistication of the genetic analysis possible in Drosophila should provide us with a wealth of information to complement the continuing studies in mice.